1. Field of the Invention
The present invention relates in general to a communication module and initialization method for a multi-air conditioner system, and more particularly to a communication module and initialization method for a multi-air conditioner system, in which one outdoor unit can control a plurality of indoor units.
2. Description of the Prior Art
An air conditioner generally comprises an evaporator, compressor, condenser and expansion valve. The evaporator is installed in an indoor unit of the air conditioner, and the compressor, condenser and expansion valve are installed in an outdoor unit of the air conditioner.
Refrigerant can be changed in state through the respective components of the air conditioner in the following manner. Namely, the refrigerant is compressed by the compressor to be changed into a high-temperature/high-pressure state. In the condenser, the high-temperature/high-pressure refrigerant exchanges heat with surrounding air to be condensed into a high-pressure liquid state. Then, the expansion valve expands the high-pressure liquid refrigerant to an evaporable state, or a low-temperature/low-pressure/low-dry state. In the evaporator, the low-temperature/low-pressure/low-dry refrigerant exchanges heat with surrounding air to be changed into a low-temperature/low-pressure vapor state, thereby lowering the temperature of room air. That is, the evaporator functions to lower the room temperature.
In a building with a large number of rooms, such as a many-storied building, there has recently been applied a multi-air conditioner system in which a plurality of indoor units are connected in common to one outdoor unit. Each of the indoor units and the outdoor unit respectively comprise their microcomputers for communicating with each other to control each other's operation. That is, the microcomputer in the outdoor unit checks operating states of the respective indoor units and determines the entire load amount in accordance with the checked results. Then, the microcomputer in the outdoor unit determines how to actuate the compressor, condenser and expansion valve in the outdoor unit, in accordance with the determined load amount. Alternatively, separate sensors may be used to sense room conditions and transmit the sensed results to the microcomputer in the outdoor unit, respectively. In this case, the microcomputer in the outdoor unit transmits control signals to the microcomputers in the indoor units in response to output signals from the separate sensors, respectively, to determine operating conditions of the indoor units.
Ultimately, an address must be assigned to each of the indoor units to allow the outdoor unit to accurately control the indoor units. The indoor units sense load amounts of the associated rooms and transmit the resultant load information to the outdoor unit, respectively, and the outdoor unit processes the load information from the respective indoor units in an integrated manner, determines how to control the respective indoor units, in accordance with the processed results, and transmits the determined results respectively to the indoor units. As a result, a communication line is required to perform the above sequential process of checking the entire load amount while exchanging information.
FIG. 1 is a block diagram showing the construction of a conventional multi-air conditioner system of a one-to-one communication type.
With reference to FIG. 1, the multi-air conditioner system comprises a plurality of indoor units 11, 12 and 13 and one outdoor unit 20. The indoor units 11, 12 and 13 include microcomputers 11a, 12a and 13a and first communication circuits 11b, 12b and 13b corresponding thereto, respectively. The outdoor unit 20 includes a microcomputer 20a and second communication circuits 21b, 22b and 23b corresponding respectively to the first communication circuits 12b, 12b and 13b in the indoor units 11, 12 and 13.
Each of the indoor units 11, 12 and 13 and the outdoor unit 20 are connected to each other in a four or three-wire manner as shown in FIG. 2. In the four-wire manner as shown in FIG. 2A, a power line and communication line each require two wires. In the three-wire manner as shown in FIG. 2B, one wire of the power line and one wire of the communication line are connected in common, resulting in the total three wires. The resultant common line is grounded.
The four-wire manner is disadvantageous in that a larger number of wires are used, resulting in an increase in material costs. For this reason, there has recently been mainly used the three-wire manner which is capable of reducing the material costs and preventing an electrical short resulting from a mis-connection between the power line and communication line.
On the other hand, in the construction of FIG. 1, the second communication circuits 21b, 22b and 23b connected to the microcomputer 20a in the outdoor unit 20 are increased in number with the indoor units 11, 12 and 13 increased in number. As a result, an increased number of communication pins must be assigned to the microcomputer 20a in the outdoor unit 20, thus making the arrangement of communication lines complex. Consequently, the installation of additional indoor units makes the communication connection complex, thereby increasing the probability of error occurrence and degrading the efficiency of communication.
In order to solve the above problems, there is required a technique in which an outdoor unit can comprise only one communication circuit for communicating with a plurality of indoor units.
FIG. 3 is a block diagram showing the construction of another conventional multi-air conditioner system.
With reference to FIG. 3, an outdoor unit and indoor units each comprise a microcomputer, power circuit and transmitter/receiver circuit. Three lines extending from each of the indoor units are connected in common to a connector in the outdoor unit. The microcomputer functions to determine how to control an associated system operation. The power circuit functions to supply a drive power to a corresponding one of the outdoor unit and indoor units. The transmitter/receiver circuit functions to transmit and receive information between the outdoor unit and the indoor units.
In the above construction, the transmitter/receiver circuit in the outdoor unit receives signals from all the indoor units when it performs a communication operation. In order to identify the indoor units transmitting the signals, the outdoor un it has to address all of them.
To this end, a system installer must personally assign addresses respectively to the indoor units after finishing the mechanical installation thereof. This is inconvenient to the system installer. Further, in the case where the user changes the addresses in use, an error may occur in the communication system.
Furthermore, in the initial process of installing the air conditioner, all the lines from the indoor units are connected to the connector in the outdoor unit. At this time, the use of many lines, or the power line, common line and communication line, may cause the lines to be erroneously connected to wrong terminals of the connector, resulting in the occurrence of a mis-wiring error as shown in FIG. 4.
For the purpose of saving the user the trouble of assigning the addresses to the indoor units, Japanese Patent Laid-open Publication No. Heisei 6-319176 shows a technique capable of automatically addressing the indoor units.
In the above technique, a microcomputer in each indoor unit generates its own address in the form of a random number, and a microcomputer in an outdoor unit sequentially calls indoor units of specific addresses and designates the indoor units respectively at the specific addresses when it receives responses therefrom. However, in the case where the same address is generated from at least two indoor units, a collision occurs on communication. A typical communication systems management association/carrier detector (CSMA/CD) method is adopted in order to overcome such a problem.
However, in the case where the CSMA/CD method is applied to the random number generation, the same address is continuously generated within a set range when the random number generation is performed again due to a collision, thereby making the normal addressing operation impossible. For example, in the case where the random number generation is limited to the range of 1 to 50 and it is again performed due to a collision between two or more indoor units at an address 49, all the indoor units generate the same random number corresponding to an address 50, resulting in a failure in addressing operation.